Rat infestation please please help!!?

Find his nest and put the poison there. Do not leave anything else out that he can eat so he will have to eat that. A dog or cat will upset the ecosystem you have out there. I have 3 cats and haven't seen a rat in ages, but on the downside they would kill the birds and frogs, and break lots of plants trying to get at everything so it might not be worth it. Good luck with your problem.